Sensor networks are a collection of devices, each with limited computing and communication capabilities, distributed over a physical area. A network collects data from its environment and typically should be able to integrate it and answer queries related to this data. Sensor networks are becoming more attractive in environmental, military and ecological applications.
The advent of sensor networks has presented a number of research challenges to the networking and distributed computation communities. Since each sensor can typically communicate only with a small number of other sensors, information generated at one sensor can reach another sensor only by routing it thru the network, whose connectivity is described by a graph. This requires ad-hoc routing algorithms, especially if the sensors are dynamic. Traditional routing algorithms rely only on the connectivity graph of the network, but with the introduction of so-called location-aware sensors, namely, those that also know what their physical location is, e.g. by being equipped with a GPS receiver, this information can be used to perform more efficient geographic routing.
In addition to routing, localization is utilized in the sensor network application itself. For most applications sensed data without spatial and temporal coordinates is of very limited use. Sensor nodes need to be aware of their location to be able to specify where a certain event has occurred. For military, police, or other radio networks, knowing the precise location of each person with a radio can be critical. In warehouses, object location and tracking applications are possible with large-scale ad-hoc networks of wireless tags. Environment monitoring, vehicle tracking and mapping are just a few other application domains where knowledge of sensor location is important. Location awareness is achieved primarily by equipping the sensors with GPS receivers. These, however, may be too expensive, too large, or too power-intense for the desired application. In indoor environments, GPS does not work at all due to the lack of line-of-sight to the satellites, so alternative solutions must be employed. Luckily, sensors are usually capable of other, more primitive, geometric measurements, which may aid in this process. An example of such a geometric measurement is the distance to neighboring sensors. This is typically achieved either by Received Signal Strength Indicator (RSSI) or Time of Arrival (ToA) techniques.
As mentioned, sensor networks are known. However, no method and system for a distributed protocol by which each sensor in a sensor network could use this local information to compute its location in some global coordinate system currently exists. As such, a localization system and method is needed for efficient localization for sensor networks. A method for utilizing location information in any of a number of sensors that is effective in the presence of noisy measurements is also desired.